Conventional economy brand caulking guns are generally manual trigger-operated devices incorporating a unidirectional gripping assembly which urges a piston rod forward to eject the compound from a cartridge. One such caulk gun is set forth in U.S. Pat. No. 5,381,931 issued to the inventor named herein for his "Caulk Dispensing Device with Multi-Position Thrust Selection Dial" (shown at FIG. 1). This patent allow the user to vary the leverage obtainable by a hand operated trigger, and insures robust delivery of the composition at a selectable volume and flow rate. The improvement helps to deliver a variety of dense fluid compounds including urethane, vinyl, polyester, epoxy and other plastics or resins.
Although delivery is important, so to is the ability to quickly cut-off delivery. Many of these compounds have other properties such as fast setting times that make them difficult to remove if excessively applied. Consequently, in addition to being robust, the dispensing device must be capable of applying a clean and uniform bead of compound, and this requires tight control over the volumetric flow rate. Optimally, control should be maintained at all times to insure a uniform bead. However, control has previously been lacking when the user wishes to reduce the bead of caulk. To do this, the user releases the trigger. Many prior art caulk guns maintain full pressure when the trigger is released and the bead of caulk continues unabated. Such lack of control can affect the quality of the bead. It is better if pressure is relieved slightly upon initial release of the trigger, momentarily slowing the flow of caulk. However, the plunger must quickly be locked in place to prevent rearward retraction and to allow the user to continue the bead. Control has also previously been lacking when the user wishes to terminate the bead of caulk. Again, the user must release the trigger and then depress a release lever to terminate the bead. This introduces a short lag time after the decision to terminate the bead. Within this lag time of maintained pressure, an unwanted surplus of compound is extruded and a messy and uneven bead often results. It is best if pressure is released upon full release of the trigger, thereby cutting off the flow of caulk.
There have been efforts to achieve this momentary releasing action in the past. For example, U.S. Pat. No. 4,566,610 issued to Herb discloses a dual-cartridge dispensing device utilizing a pair of angled grips 16 (see FIG. 1) which engage a releasing member 19 upon full release of the trigger to thereby remove all driving force and flee the plunger shafts. Unfortunately, the releasing mechanism of Herb '610 is adapted for that particular drive assembly, and the drive assembly is complex and expensive.
U.S. Pat. No. 4,461,407 to Finnegan discloses an automatic pressure relief mechanism for a caulk gun including an annular elastic ring 42 tightly encircling the plunger shaft 8. The ring 42 is held against the interior of housing 21 by a fixed retainer 200. When the trigger 130 is retracted, the plunger shaft 124 is urged forward through the ring 42. Since it is tight, the ring deforms and is partially pulled through the housing wall 21. When the trigger 130 is released, the deformed ring 42 tries to regain its shape, thereby pulling shaft 124 back a bit. This releases pressure, and a dripstop feature is introduced. Despite the advantage, the Finnegan '407 caulk gun has its drawbacks. Specifically, the attachment of the frictional ring 42 to the wall of housing 21 impedes the motion of the plunger shaft 124. The elastic ring 42 becomes the subject of deformation and wear. Moreover, the ring 42 and retainer 200 assembly is rather costly as it requires intricate metal forming (see FIG. 2), welding (column 4, lines 24-26), and a precision-fit elastic ring (see column 4, lines 63-68). These factors escalate the manufacturing costs.
U.S. Pat. No. 5,156,305 to Eyre discloses a drive assembly for a more economical molded-plastic open frame caulk gun. In this open frame type (see FIG. 2), the plunger shaft is slidably carried by two sleeves 28, 30 formed in a molded plastic housing. A downwardly extending trigger 43 is pivoted to the housing and retractable against the handle 46. The trigger 43 includes an upper rivet 45 above the pivot point. The upper rivet 45 bears against a first gripping member 41 that encircles the plunger shaft, and a compression spring 42 rearwardly biases the first gripping member 41 toward the trigger 43. A release lever 51 encircles the plunger shaft and extends upwardly behind the housing to a pivot point. Like Finnegan '407, Eyre '305 also teaches the use of a rod-engaging O-ring bush 52 that relieves pressure upon release of the trigger. In contrast to Finnegan '407, Eyre '305 attaches the bush 52 to the release lever 51 to move therewith (see, also, column 4, lines 18). The plunger shaft fictionally passes through the elastic bush 52. In operation, the release lever 51 with integral bush 52 rides forward on the plunger shaft while the trigger 43 is retracted. When the trigger 43 is first released, the friction of the bush 52 catches the plunger shaft and the release lever 51 is carried backward. The release lever 51 eventually attains a critical angle and engages the plunger shaft to prevent further retraction. However, pressure is released in the meantime, and a dripstop feature is introduced. As did Finnegan '407, Eyre '305 also leaves room for improvement. However, the bush 52 and housing 53 assembly is rather costly as it requires drilling of a hole through the release lever, insertion of the bush 52 in the housing 53, and insertion of the combination into the release lever hole. The additional parts and labor greatly increases manufacturing costs.
The present inventor has in the past developed various mechanisms which would insure an operating range (short of full release) where the plunger shaft cannot retract and pressure is maintained. This way, an operator can selectively keep the trigger within the operating range to apply/maintain pressure and output a uniform bead of caulk. Alternatively, the operator can fully release the trigger to release pressure, end the bead, and stop dripping. However, there remains room for improvement. There are situations where the user may wish to release the trigger yet not remove pressure (to maintain a continuous and even bead of caulk). This ability does not exists with any of the above-described prior art patents. Consequently, it is most desirable to give the user the option of completely disengaging or not upon full release of the trigger. Furthermore, when the trigger is fully released and pressure is removed, the freedom of the plunger shaft to slide has proven to be a safety hazard in certain situations. For example, when the user is atop a ladder doing overhead caulking, it is obviously best if the plunger shaft were restrained against rearward sliding after release of the trigger. The freedom of the plunger shaft also makes it difficult to hang the gun by hooked end of the shaft from a ladder or window sill. The gravity of the gun tends to pull out the plunger shaft. However, any proposed solutions should not effect the incremental extension of the gun and drive efficiency, nor should it escalate the manufacturing costs.